Difference between revisions of "cpp/algorithm/ranges/generate n"
From cppreference.com
m (→Parameters: '.') |
m (→See also: +generate_random.) |
||
| (3 intermediate revisions by 3 users not shown) | |||
| Line 2: | Line 2: | ||
{{cpp/algorithm/ranges/navbar}} | {{cpp/algorithm/ranges/navbar}} | ||
{{dcl begin}} | {{dcl begin}} | ||
| − | {{dcl header | algorithm}} | + | {{dcl header|algorithm}} |
| − | {{dcl h | Call signature}} | + | {{dcl h|Call signature}} |
| − | {{dcl | + | {{dcl|since=c++20|1= |
| − | template<std::input_or_output_iterator O, std::copy_constructible F> | + | template< std::input_or_output_iterator O, std::copy_constructible F > |
| − | + | requires std::invocable<F&> && std::indirectly_writable<O, std::invoke_result_t<F&>> | |
| − | + | constexpr O | |
| + | generate_n( O first, std::iter_difference_t<O> n, F gen ); | ||
}} | }} | ||
{{dcl end}} | {{dcl end}} | ||
| − | Assigns the result of ''successive'' invocations of the function object {{ | + | Assigns the result of ''successive'' invocations of the function object {{c|gen}} to each element in the range {{range|first|first + n}}, if {{c|0 < n}}. Does nothing otherwise. |
{{cpp/ranges/niebloid}} | {{cpp/ranges/niebloid}} | ||
| Line 17: | Line 18: | ||
===Parameters=== | ===Parameters=== | ||
{{par begin}} | {{par begin}} | ||
| − | {{par | first | the beginning of the range of elements to modify}} | + | {{par|first|the beginning of the range of elements to modify}} |
| − | {{par | n | number of elements to modify}} | + | {{par|n|number of elements to modify}} |
| − | {{par | gen | the generator function object.}} | + | {{par|gen|the generator function object.}} |
{{par end}} | {{par end}} | ||
===Return value=== | ===Return value=== | ||
| − | Iterator one past the last element assigned if {{c|0 < count}}, {{ | + | Iterator one past the last element assigned if {{c|0 < count}}, {{c|first}} otherwise. |
===Complexity=== | ===Complexity=== | ||
| − | Exactly {{c|n}} invocations of {{ | + | Exactly {{c|n}} invocations of {{c|gen()}} and assignments. |
===Possible implementation=== | ===Possible implementation=== | ||
| − | {{eq fun | 1= | + | {{eq fun|1= |
| − | struct generate_n_fn { | + | struct generate_n_fn |
| − | + | { | |
| + | template<std::input_or_output_iterator O, std::copy_constructible F> | ||
requires std::invocable<F&> && std::indirectly_writable<O, std::invoke_result_t<F&>> | requires std::invocable<F&> && std::indirectly_writable<O, std::invoke_result_t<F&>> | ||
| − | + | constexpr O operator()(O first, std::iter_difference_t<O> n, F gen) const | |
| − | for (; n-- > 0; *first = std::invoke(gen), ++first) | + | { |
| + | for (; n-- > 0; *first = std::invoke(gen), ++first) | ||
| + | {} | ||
return first; | return first; | ||
| − | + | } | |
}; | }; | ||
| − | inline constexpr generate_n_fn generate_n{}; | + | inline constexpr generate_n_fn generate_n {}; |
}} | }} | ||
| Line 50: | Line 54: | ||
#include <string_view> | #include <string_view> | ||
| − | auto dice() { | + | auto dice() |
| − | static std::uniform_int_distribution<int> distr{1, 6}; | + | { |
| + | static std::uniform_int_distribution<int> distr {1, 6}; | ||
static std::random_device engine; | static std::random_device engine; | ||
| − | static std::mt19937 noise{engine()}; | + | static std::mt19937 noise {engine()}; |
return distr(noise); | return distr(noise); | ||
} | } | ||
| − | void print(const auto& v, std::string_view comment) { | + | void print(const auto& v, std::string_view comment) |
| − | for (int i : v) | + | { |
| − | std::cout << | + | for (int i : v) |
| + | std::cout << i << ' '; | ||
| + | std::cout << '(' << comment << ")\n"; | ||
} | } | ||
| Line 69: | Line 76: | ||
print(v, "dice"); | print(v, "dice"); | ||
| − | std::ranges::generate_n(v.begin(), v.size(), [n{0}] | + | std::ranges::generate_n(v.begin(), v.size(), [n {0}] mutable { return n++; }); |
// same effect as std::iota(v.begin(), v.end(), 0); | // same effect as std::iota(v.begin(), v.end(), 0); | ||
print(v, "iota"); | print(v, "iota"); | ||
} | } | ||
| − | + | |p=true | |
| − | + | |output= | |
5 5 2 2 6 6 3 5 (dice) | 5 5 2 2 6 6 3 5 (dice) | ||
0 1 2 3 4 5 6 7 (iota) | 0 1 2 3 4 5 6 7 (iota) | ||
| Line 81: | Line 88: | ||
===See also=== | ===See also=== | ||
{{dsc begin}} | {{dsc begin}} | ||
| − | {{dsc inc | cpp/algorithm/ranges/dsc generate}} | + | {{dsc inc|cpp/algorithm/ranges/dsc generate}} |
| − | {{dsc inc | cpp/algorithm/ranges/dsc fill}} | + | {{dsc inc|cpp/numeric/random/ranges/dsc generate_random}} |
| − | {{dsc inc | cpp/algorithm/ranges/dsc fill_n}} | + | {{dsc inc|cpp/algorithm/ranges/dsc fill}} |
| − | {{dsc inc | cpp/algorithm/ranges/dsc transform}} | + | {{dsc inc|cpp/algorithm/ranges/dsc fill_n}} |
| − | {{dsc inc | cpp/algorithm/dsc | + | {{dsc inc|cpp/algorithm/ranges/dsc transform}} |
| + | {{dsc inc|cpp/algorithm/dsc generate_n}} | ||
{{dsc end}} | {{dsc end}} | ||
{{langlinks|de|es|fr|it|ja|pt|ru|zh}} | {{langlinks|de|es|fr|it|ja|pt|ru|zh}} | ||
Latest revision as of 14:55, 17 April 2024
| Defined in header <algorithm>
|
||
| Call signature |
||
| template< std::input_or_output_iterator O, std::copy_constructible F > requires std::invocable<F&> && std::indirectly_writable<O, std::invoke_result_t<F&>> |
(since C++20) | |
Assigns the result of successive invocations of the function object gen to each element in the range [first, first + n), if 0 < n. Does nothing otherwise.
The function-like entities described on this page are niebloids, that is:
- Explicit template argument lists cannot be specified when calling any of them.
- None of them are visible to argument-dependent lookup.
- When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.
In practice, they may be implemented as function objects, or with special compiler extensions.
Contents |
[edit] Parameters
| first | - | the beginning of the range of elements to modify |
| n | - | number of elements to modify |
| gen | - | the generator function object. |
[edit] Return value
Iterator one past the last element assigned if 0 < count, first otherwise.
[edit] Complexity
Exactly n invocations of gen() and assignments.
[edit] Possible implementation
struct generate_n_fn { template<std::input_or_output_iterator O, std::copy_constructible F> requires std::invocable<F&> && std::indirectly_writable<O, std::invoke_result_t<F&>> constexpr O operator()(O first, std::iter_difference_t<O> n, F gen) const { for (; n-- > 0; *first = std::invoke(gen), ++first) {} return first; } }; inline constexpr generate_n_fn generate_n {}; |
[edit] Example
Run this code
#include <algorithm> #include <array> #include <iostream> #include <random> #include <string_view> auto dice() { static std::uniform_int_distribution<int> distr {1, 6}; static std::random_device engine; static std::mt19937 noise {engine()}; return distr(noise); } void print(const auto& v, std::string_view comment) { for (int i : v) std::cout << i << ' '; std::cout << '(' << comment << ")\n"; } int main() { std::array<int, 8> v; std::ranges::generate_n(v.begin(), v.size(), dice); print(v, "dice"); std::ranges::generate_n(v.begin(), v.size(), [n {0}] mutable { return n++; }); // same effect as std::iota(v.begin(), v.end(), 0); print(v, "iota"); }
Possible output:
5 5 2 2 6 6 3 5 (dice) 0 1 2 3 4 5 6 7 (iota)
[edit] See also
| (C++20) |
saves the result of a function in a range (niebloid) |
| (C++26) |
fills a range with random numbers from a uniform random bit generator (niebloid) |
| (C++20) |
assigns a range of elements a certain value (niebloid) |
| (C++20) |
assigns a value to a number of elements (niebloid) |
| (C++20) |
applies a function to a range of elements (niebloid) |
| assigns the results of successive function calls to N elements in a range (function template) |
